1. Field of the Invention
The present invention relates to a vertical treatment apparatus which is capable of performing heat treatment while simultaneously measuring the temperature in a reaction furnace with high accuracy.
2. Description of the Related Art
In the field of manufacture of semiconductor devices, a vertical heat treatment apparatus is employed as a CVD apparatus (which is used for forming a thin film, such as an oxide film), an epitaxial apparatus, a thermal diffusion apparatus, etc. In the vertical heat treatment apparatus, a plurality of semiconductor wafers, for example 100, are mounted on a wafer boat in a horizontal state such that they are located away from adjacent ones by a predetermined distance. These semiconductor wafers are heat treated in a batchwise operation at high temperature, for example, between 800.degree. C. and 1,000.degree. C.
FIG. 1 shows an example of a conventional heat treatment apparatus. As is shown in FIG. 1, a tubular heating device 11 is arranged around a reaction tube 10, to thereby constitute a reaction furnace. The heating device 11 is made up of an upper heater 11a, an intermediate heater 11b, and a lower heater 11c in order to define the uniformly-heated region extensively, and these heaters heat the interval reaction tube 10 at a desirable temperature between 500.degree. C. and 1,200.degree. C. The reaction furnace is arranged substantially vertical, and is surrounded with a heat insulator 12. A wafer boat 14 is located inside the reaction tube 10 of the reaction furnace, and a large number of semiconductor wafers 13 are arranged in the wafer boat 14 at predetermined intervals in the vertical direction such that each wafer is kept in a horizontal state. The wafer boat 14 is mounted on a turntable 25, which is coupled to a rotating mechanism located outside of the reaction furnace, and can be moved up or down by a conveyance mechanism (not shown), together with the rotating mechanism. The uniform heating is performed by rotating the wafer boat 14 using the rotating mechanism.
A gas supply port 16, through which a reaction gas is supplied into the reaction tube 10, is formed in the top wall of the reaction tube 10. One end of a gas pipe 15 is connected to the ga supply port 16, while the other end thereof is connected to gas supply means (not shown). A gas exhaust port 17, through which a gas is exhausted from the reaction tube 10, is located at a lower portion of the side wall of the reaction tube 10. The gas exhaust port 17 is connected to gas exhaust means (not shown).
The heat insulator 12 has a plurality of through-holes 18, and a thermocouple 19 is inserted in each through-hole 18. The thermocouple 19 can measure the temperature of the outer wall of the reaction tube 10 from outside, with its temperature-measuring end being in contact with the outer wall. That end which is opposite to the temperature-measuring end is connected to control means (not shown).
Published Examined Japanese Patent Application (PEJPA) No. 60-46787 and Published Unexamined Japanese Utility Model Application (PUJUMA) No. 62-142841 each disclose a heat treatment apparatus which enables measurement of the temperature in the interior of the reaction tube 10. In the heat treatment apparatus, a thin quartz pipe is arranged inside the reaction tube, and a rod-shaped thermocouple serving as a temperature sensor is inserted in the quartz pipe.
However, such a thin quartz pipe cannot be fixed inside the reaction tube of a vertical heat treatment apparatus. In the vertical heat treatment apparatus, the upper region of the reaction tube is closed, and the lower region thereof is used for getting a quartz wafer boat (in which a large number of semiconductor wafers are arranged) in and out. If a thin quartz pipe is fixed inside the reaction tube, it may become an obstacle to the installation or removal of the wafer boat. In addition, it narrows the utilizable reaction region in the reaction tube. If the utilizable reaction region in the reaction tube is narrowed, its central axis is shifted from the central axis of the array of the semiconductor wafers arranged in the wafer boat, thus causing disadvantages with respect to the loading of the wafer boat.
Residues of reaction products adhere to the inner wall of the reaction tube during the process of reaction. Thus, the inner wall of the reaction tube is required to be cleaned of such residues by washing the reaction tube several times a month, for example. Usually, the reaction tube is washed by removing it from the heat treatment apparatus and immersing it in a hydrofluoric acid or the like. Since the reaction tube is washed in this way, the thermocouple has to be removable from the reaction tube at the time of washing the reaction tube. If the thermocouple is immovably fixed inside the reaction tube, it is not possible to wash the reaction tube.
Since a thermocouple cannot be immovably fixed inside the reaction tube, as mentioned above, there has been no vertical heat treatment apparatus available which is capable of performing heat treatment while simultaneously measuring the temperature in the interior of the reaction tube.
Conventionally, the temperature in the interior of the reaction tube in which heat treatment is in progress has been determined as follows. First, a temperature sensor incorporating a thermocouple is inserted into the reaction tube before staring heat treatment, and the temperature in the interior of the reaction tube is increased. When the temperature of the sensor has reached a predetermined value, the temperature of the outer wall of the reaction tube is measured, and the relationships between the temperature in the interior of the reaction tube and the temperature of the outer wall of the reaction tube are calculated. On the basis of the temperature relationships, the temperature in the interior of the reaction tube in which heat treatment is in progress is estimated from the temperature of the outer output of the wall of the reaction tube. Subsequently, the output of the heater is controlled in accordance with the estimated temperature, to thereby control the temperature in the interior of the reaction tube.
The temperature control mentioned above is performed on the basis of the estimation of the temperature in the interior of the reaction tube. Therefore, the temperature control is not always performed with precision.